5-4
TROUBLESHOOTING
ORBAN MODEL 8300
Interference from stereo into SCA
A properly operating 8300 generates an immaculately clean baseband, with pro-
gram-correlated noise below –80 dB above 57 kHz even when the composite limiter
is used aggressively. If the 8300 and the rest of the transmission system are operat-
ing correctly, subcarriers should experience no interference.
Interference from the stereo into a subcarrier is best diagnosed with a spectrum
analyzer. First examine the spectrum of the 8300’s composite output to verify that
program correlated noise is
less than –80 dB below
100% modulation from 57
to 100 kHz. Any inadvertent
composite clipping will dra-
matically degrade this pro-
tection. Make sure that the
link between the 8300’s
composite output and the
transmitter has sufficient
headroom.
If the exciter is nonlinear,
this can cause crosstalk. In
general, a properly operat-
ing exciter should have less
than 0.1% THD at high fre-
quencies to achieve correct
operation with subcarriers.
To prevent truncation of the higher-order Bessel sidebands of the FM modulation,
the RF system following the exciter must be wideband (better than
500 kHz) and
must have symmetrical group delay around the carrier frequency. An incorrectly
tuned transmitter can exhibit an asymmetrical passband that will greatly increase
crosstalk into subcarriers.
Amplitude modulation of the carrier that is synchronous with the program (“syn-
chronous AM”) can cause program-related crosstalk into subcarriers. Synchronous
AM should be better than 35 dB below 100% modulation as measured on a syn-
chronous AM detector with standard FM de-emphasis (50
s or 75
s).
The subcarrier receiver itself must receive a multipath-free signal, and must have a
wide and symmetrical IF passband and a linear, low-distortion FM demodulator to
prevent program-related crosstalk into subcarriers.
Shrill, Harsh Sound
If you are using the Multi-Band structure, this problem can be caused by excessive
HF boost in the HF Equalizer and HF Enhancer. It could also be caused by an exces-
sively high setting of the
BAND
4
THRESH
control, or by excessively high settings of
the
BAND
4
MIX
and
BAND
5
MIX
controls (located in Intermediate and Advanced
Modify).
SRS
57.088 kHz
-72.881
dBVpk
0 Hz
FFT 1 Log Mag BMH
PkhAvg
20000
51.2 kHz
102.4 kHz
-100
dBVpk
0
dBVpk
10
dB/div
Fig. 5-1: Typical 8300 baseband spectrum with heavy
processing, 0-100 kHz.
Summary of Contents for 8300J
Page 1: ...Operating Manual OPTIMOD FM 8300 Digital Audio Processor Version 2 1 Software...
Page 7: ...Operating Manual OPTIMOD FM 8300 Digital Audio Processor Version 2 1 Software...
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Page 247: ...OPTIMOD FM DIGITAL TECHNICAL DATA 6 29...
Page 254: ...6 36 TECHNICAL DATA ORBAN MODEL 8300 CPU Module...
Page 260: ...6 42 TECHNICAL DATA ORBAN MODEL 8300 8300 RS232 BOARD PARTS LOCATOR...
Page 262: ...6 44 TECHNICAL DATA ORBAN MODEL 8300 8300 POWER SUPPLY PARTS LOCATOR...
Page 264: ...6 46 TECHNICAL DATA ORBAN MODEL 8300 8300 I O BOARD PARTS LOCATOR...
Page 270: ...6 52 TECHNICAL DATA ORBAN MODEL 8300 DSP BOARD PARTS LOCATOR DRAWING 32170 000 14...
Page 278: ...6 60 TECHNICAL DATA ORBAN MODEL 8300 8300 DISPLAY BOARD PARTS LOCATOR...
Page 279: ...OPTIMOD FM DIGITAL TECHNICAL DATA 6 61 DISPLAY BOARD...